This being said, at least some years ago, a use case I saw that held SOME water then was generating MyISAM tables offline, importing them as-is into a running MySQL (or taking an instance offline and bringing it back up) and then serving from it read-only. At least at the time, this provided better RO performance than InnoDB. I wouldn't be surprised if that was still true. Please don't do that at home!
Also, I think until the previous-to-most-recent release, some internal tables were still MyISAM, causing MySQL overall to have some very rare cases of not being crash safe. Again, I think that's since been resolved in 5.8(?).
Is there any reason to ever use it
Google "ibdata1 one file per table" to see all the pain it causes.
> But it does not seperate table data into one file per table
That's because if you didn't have it set when creating the database, it won't move data to the new fs layout when you set the setting on, without an OPTIMIZE. If you had it on from the beginning, table data is per file. I literally just did an ls on my /va/lib/mysql and there's a folder per database, in which there are 2 files per table (.frm and .ibd).
When innodb_file_per_table is on, and the database has been OPTIMIZEd, only the following is stored in ibdata1 [0]:
- data dictionary aka metadata of InnoDB tables
- change buffer
- doublewrite buffer
- undo logs
[0] https://www.percona.com/blog/2013/08/20/why-is-the-ibdata1-f...
only the following is stored in ibdata1
Just look at the very page you linked to. It's a totally confusing concept that befuddles users and causes questions "we often receive", starts "panic", can "unfortunately" not easily be analyzed and you might need to "kill threads" and initiate "rollbacks" to fix the problems it brings.
MyISAM got that right. One dir per database.
You should mostly treat it as a black box